Schuster Martin, Kilaru Sreedhar, Wösten Han A B, Steinberg Gero
Department of Biosciences, University of Exeter, Exeter, United Kingdom.
Microbiology, Department of Biology, University of Utrecht, Utrecht, The Netherlands.
Nat Commun. 2025 May 12;16(1):4402. doi: 10.1038/s41467-025-59606-4.
Filamentous fungi colonise substrates by invasive growth of multi-cellular hyphae. It is commonly accepted that hyphae expand by tip growth that is restricted to the first apical cell, where turgor pressure, exocytosis and endocytosis cooperate to expand the apex. Here we show that, contrary to expectations, subapical cells play important roles in hyphal growth in the industrial enzyme-producing fungus Trichoderma reesei. We find that the second and third cells are crucial for hyphal extension, which correlates with tip-ward cytoplasmic streaming, and the fourth-to-sixth cells support rapid growth rates. Live cell imaging reveals exocytotic and endocytic activity in both apical and subapical cells, associated with microtubule-based bi-directional transport of secretory vesicles and early endosomes across septa. Moreover, visualisation of 1,3-β-glucan synthase in subapical cells reveals that these compartments deliver cell wall-forming enzymes to the apical growth region. Thus, subapical cells are active in exocytosis and endocytosis, and deliver growth supplies and enzymes to the expanding hyphal apex.
丝状真菌通过多细胞菌丝的侵入性生长来定殖基质。人们普遍认为，菌丝通过顶端生长进行扩展，这种生长仅限于第一个顶端细胞，在该细胞中，膨压、胞吐作用和内吞作用共同作用以使顶端扩展。在这里，我们表明，与预期相反，在工业酶生产真菌里氏木霉中，亚顶端细胞在菌丝生长中发挥着重要作用。我们发现，第二和第三个细胞对菌丝延伸至关重要，这与向顶端的细胞质流动相关，而第四至第六个细胞则支持快速生长速率。活细胞成像显示顶端和亚顶端细胞中均存在胞吐和内吞活动，这与基于微管的分泌囊泡和早期内体跨隔膜的双向运输有关。此外，对亚顶端细胞中1,3-β-葡聚糖合酶的可视化显示，这些区室将细胞壁形成酶输送到顶端生长区域。因此，亚顶端细胞在胞吐和内吞作用中具有活性，并将生长所需物质和酶输送到不断扩展的菌丝顶端。
